Spark Plugs

The spark plugs should be replaced every 15,000 miles (1973-79) or 30,000 miles (1980-83).

Most people know that the spark plug ignites the air/fuel mixture in the cylinder, which in turn forces the piston downward, turning the crankshaft. This action turns the drivetrain (clutch, transaxle, drive axles) and moves the vehicle. What many people do not know, however, is that spark plugs should be chosen according to the type of driving done. The plug with a long insulator nose retains heat long enough to burn off oil and combustion deposits under light engine load conditions. A short-nosed plug dissipates heat rapidly and prevents pre-ignition and detonation under heavily loaded conditions. Under normal driving conditions, a standard plug is just fine.

Fig. Fig. 1: Spark plug cross-section

Fig. Fig. 2: Spark plug information label on valve cover

Spark plug life is largely governed by operating conditions and varies accordingly. To ensure peak performance, inspect the plugs every 10,000-15,000 miles. Faulty or excessively worn plugs should be replaced immediately. It is also helpful to check plugs for types of deposit and degree of electrode wear, as an indication of engine operating condition. Excessive or oily deposits could be an indication of real engine trouble, it would be wise to investigate the problem thoroughly and make sure the cause is found and corrected.

REMOVAL & INSTALLATION

See Figures 3 through 7

Disconnect the negative battery cable. Place a piece of masking tape around each spark plug wire and number it according to its corresponding cylinder.

Pull the wire from the spark plug, grasping the wire by the end of the rubber boot and twisting off. It is recommended that the spark plugs be replaced one at a time. This will help prevent installing the wires in the incorrect order.

Avoid spark plug removal while the engine is Hot. Since the cylinder head spark plug threads are aluminum, the spark plug becomes tight due to the different coefficients of heat expansion. If a plug is too tight to be removed even while the engine is Cold, apply a solvent around the plug followed with an application of oil once the solvent has penetrated the threads. Do this only when the engine is
Cold.

Loosen each spark plug with a
13
/
16
inch spark plug socket. When the plug has been loosened a few turns, stop to clean any material from around the spark plug holes; compressed air is preferred. If air is not available, simply use a rag to clean the area.

In no case should foreign material be allowed to enter the cylinders. Severe damage could result.

Remove and inspect the spark plugs; if necessary, clean them.

To install:

Inspect and set the spark plug gap to specifications. Refer to the Tune-Up Specifications Chart'' listed in this Section.

Oil the spark plug threads and hand tighten them into the cylinder head. Torque the spark plugs into the cylinder head to 13 ft. lbs.

It's a good idea to apply an anti-seize compound on the threads of the spark plugs before installing them. DO NOT over-tighten them because of the aluminum cylinder heads.

Connect the wires to the plugs, making sure that each is securely fitted. Reconnect the battery cable.

Fig. Fig. 3: A variety of tools and gauges are needed for spark plug service

Fig. Fig. 4: Mark and remove the spark plug wire

Fig. Fig. 5: Removing the spark plug

Fig. Fig. 6: Checking the spark plug gap with a feeler gauge

Fig. Fig. 7: Adjusting the spark plug gap

INSPECTION AND CLEANING

Before attempting to clean and re-gap plugs be sure that the electrode ends are not worn or damaged and that the insulators (the white porcelain covering) are not cracked; replace the plug if this condition exists.

Clean reusable plugs with a small file or a wire brush. The plug gap should be checked and readjusted, if necessary, by bending the ground electrode with a spark plug gapping tool.

DO NOT use a flat gauge to check plug gap. An incorrect reading will result; use a wire gauge only. Also, replace the plugs one at a time, keeping the ignition wires connected to those plugs you're not working on. This will avoid confusion about how to reconnect the plug wires according to the firing order.